What is the game for playstation 1 with multiple CD's that involves a boy fighting shadows as enemies?

I remember the very beginning played a cutscene where the boy was being thrown into a cabinet by his teacher at his school, then running home to his treehouse (or something like one) with his dog. Later, his dog suddenly goes missing at night. I'm quite sure the game had somewhere around 2 to maybe even 4 discs total because the game was so long. It was a sidescroller too, and these creepy shadows were always attacking you. The only weapon you had (as far as i knew) was this little electric gun the boy made (I think). I'm sorry if this isn't enough information but any kind of help is welcome. I haven't played this game in maybe 10 years but I'd really like to play all my young childhood games again (even though I remember this one was ridiculously hard) so thanks in advance.